201 research outputs found
Intelligent Reflecting Surfaces: Sum-Rate Optimization Based on Statistical CSI
In this paper, we consider a multi-user multiple-input multiple-output (MIMO)
system aided by multiple intelligent reflecting surfaces (IRSs) that are
deployed to increase the coverage and, possibly, the rank of the channel. We
propose an optimization algorithm to configure the IRSs, which is aimed at
maximizing the network sum-rate by exploiting only the statistical
characterization of the environment, such as the distribution of the locations
of the users and the distribution of the multipath channels. As a consequence,
the proposed approach does not require the estimation of the instantaneous
channel state information (CSI) for system optimization, thus significantly
relaxing (or even avoiding) the need of frequently reconfiguring the IRSs,
which constitutes one of the most critical issues in IRS-assisted systems.
Numerical results confirm the validity of the proposed approach. It is shown,
in particular, that IRS-assisted wireless systems that are optimized based on
statistical CSI still provide large performance gains as compared to the
baseline scenarios in which no IRSs are deployed.Comment: submitted for journal publicatio
System-Level Modelling and Beamforming Design for RIS-assisted Cellular Systems
Reconfigurable intelligent surface (RIS) is considered as key technology for
improving the coverage and network capacity of the next-generation cellular
systems. By changing the phase shifters at RIS, the effective channel between
the base station and user can be reconfigured to enhance the network capacity
and coverage. However, the selection of phase shifters at RIS has a significant
impact on the achievable gains. In this letter, we propose a beamforming design
for the RIS-assisted cellular systems. We then present in detail the
system-level modelling and formulate a 3-dimension channel model between the
base station, RIS, and user, to carry out system-level evaluations. We evaluate
the proposed beamforming design in the presence of ideal and discrete phase
shifters at RIS and show that the proposed design achieves significant
improvements as compared to the state-of-the-art algorithms
Memory-Enhanced Dynamic Evolutionary Control of Reconfigurable Intelligent Surfaces
An innovative evolutionary method for the dynamic control of reconfigurable
intelligent surfaces (RISs) is proposed. It leverages, on the one hand, on the
exploration capabilities of evolutionary strategies and their effectiveness in
dealing with large-scale discrete optimization problems and, on the other hand,
on the implementation of memory-enhanced search mechanisms to exploit the
time/space correlation of communication environments. Without modifying the
base station (BS) beamforming strategy and using an accurate description of the
meta-atom response to faithfully account for the micro-scale EM interactions,
the RIS control (RISC) algorithm maximizes the worst-case throughput across all
users without requiring that the Green's partial matrices, from the BS to the
RIS and from the RIS to the users, be (separately) known/measured.
Representative numerical examples are reported to illustrate the features and
to assess the potentialities of the proposed approach for the RISC
Intelligent Omni-Surfaces for Full-Dimensional Wireless Communications: Principle, Technology, and Implementation
The recent development of metasurfaces has motivated their potential use for
improving the performance of wireless communication networks by manipulating
the propagation environment through nearly-passive sub-wavelength scattering
elements arranged on a surface. However, most studies of this technology focus
on reflective metasurfaces, i.e., the surface reflects the incident signals
towards receivers located on the same side of the transmitter, which restricts
the coverage to one side of the surface. In this article, we introduce the
concept of intelligent omni-surface (IOS), which is able to serve mobile users
on both sides of the surface to achieve full-dimensional communications by
jointly engineering its reflective and refractive properties. The working
principle of the IOS is introduced and a novel hybrid beamforming scheme is
proposed for IOS-based wireless communications. Moreover, we present a
prototype of IOS-based wireless communications and report experimental results.
Furthermore, potential applications of the IOS to wireless communications
together with relevant research challenges are discussed
- …